Significant development activity has been directed toward eliminating the costly, labor intensive cut and sew method of wrapping fabric about a cellular foam pad in automotive seat fabrications. One such development employs contact adhesives applied to the fabric layer, i.e., spray adhesive, and the foam pad to adhesively bond them together. However, once the adhesive is applied, it is difficult to properly position the fabric onto the foam pad resulting in misalignment and/or wrinkles in the bonded fabric.
Other developments have included placing a heat-sensitive adhesive fabric or film between the fabric and the foam pads and subsequently melting the adhesive to effectuate bonding. One known technique for melting the adhesive employs a heated compression mold in contact with the fabric layer to conduct heat through the fabric layer which, in turn, melts the adhesive. In addition to being time consuming, this technique causes non-uniform bonding due to an uneven temperature distribution throughout the adhesive. Additionally, many fabric types which are otherwise well suited for seating applications are made from materials which cannot withstand the high temperature ranges encountered with this technique, i.e., leather and vinyl, thus rendering unusable these otherwise desirable materials.
Another technique for heating and melting the adhesive film uses heated steam injected through either the fabric layer or the foam pad to melt the adhesive. Such a technique is disclosed in U.S. Pat. No. 4,692,199 to Kozlowski et al, assigned to the assignee of the subject invention. As discussed above, certain cover fabrics are sensitive to high temperature environments and may be damaged by the injection of heated steam.
U.S. Pat. No. 5,254,197, assigned to the assignee of the subject invention, discloses adhesively bonding a fabric layer to a cellular foam pad using a heat sensitive adhesive placed therebetween wherein melting of the adhesive is accomplished by utilizing a microwave radiation source which selectively heats and melts the adhesive without damaging the cushion or seat fabric. A problem with this system is that use of microwave heating requires additional time in processing due to transfer of the assembly to the microwave heater, and the requirement of high frequency requires shielding.
Magnetic induction bonding has been utilized for bonding a joint between two substrates. Japanese Patent Numbers 4-261,691 and 4-261,692, both disclose methods for magnetic induction bonding of seat fabrics to cushion pads via the use of hot melt bonding agents containing metallic material. Each of these methods disclose use of a mold having a seat cushion placed thereon. The seat cushion is coated with a hot melt bonding agent during foaming of the pad. A fabric is then placed over the bonding agent and cushion. The bonding agent is melted via electromagnetic induction while the fabric skin is compressed against the seat cushion. The hot melt adhesive includes metallic material, such as iron, stainless steel, lead, etc. The metallic material may be in the form of foil, powder, or granules. The patent specifically discloses using a sheet of foil with the hot melt adhesive on both sides thereof. The bottom die supports the molded pad whereas the top die is hollow to hold the electromagnetic coil and cooling air. The cooling air is forced through the upper die after heating to cool the melted adhesive.
Magnetic induction bonding processes are also illustrated in Japanese Patent Numbers 59-173619 and 2-167726, and U.S. Pat. Nos. 3,833,439 to Smith and 4,941,936 to Wilkinson et al.
U.S. Pat. Nos. 3,902,940 to Heller, Jr. et al and Patent Number 4,969,968 and 5,129,977, both to Leatherman, also disclose methods for the magnetic induction bonding of component parts wherein the parts are bonded via the placement of the adhesive film or coating between the component parts. The adhesive film or coating contains at least ferromagnetic particles in a thermoplastic matrix or medium. The adhesive is melted via micromagnetic radiation to fuse the component parts together.
U.S. Pat. No. 3,657,038 to Lightfoot discloses a method for magnetic induction bonding of two substrates via use of an adhesive composition comprising, in at least one embodiment, ferromagnetic particles in a polyamide.
None of these processes provide a cost effective and simple method of applying a seat cover to a foam pad. Seat covers of various materials must be bonded to foam pads with suitable cohesive failure properties. The subject invention allows accurate positioning and simple assembly of the components to allow for bonding the seat cover to the foam pad.